Drag-free Spacecraft Technologies: criticalities in the initialization of geodesic motion

TL;DR

This paper discusses the challenges and solutions in initializing drag-free spacecraft for missions like LISA-Pathfinder, focusing on test mass release, disturbance mitigation, and system design to improve mission reliability.

Contribution

It provides experimental insights and preliminary design considerations for the test mass housing, enhancing technology maturity for future drag-free space missions.

Findings

Experimental studies on test mass release in simulated flight conditions.

Identification of critical phenomena affecting drag-free initialization.

Design proposals for low-cost test mass housing.

Abstract

Present and future space missions rely on systems of increasingly demanding performance for being successful. Drag-free technology is one of the technologies that is fundamental for LISA-Pathfinder, an ESA mission whose launch is planned for the end of September 2015. A purely drag-free object is defined by the absence of all external forces other than gravity. This is not a natural condition and thus requires a proper design of a spacecraft, whose core is an object in free-fall, called test mass (TM). The purity of the drag-free orbit depends on the spacecraft capability of protecting the TM from disturbances, which indeed has limitations. According to a NASA study, such a concept provides substantial economies for LEO satellites. At the same time, a drag-free motion is required in many missions of fundamental physics. eLISA is an ESA concept mission aimed at opening a new window to the universe, black holes, and massive binary systems by means of gravitational waves. LISA-Pathfinder is in charge of proving the eLISA concept. In this frame, the system holding the TM during launch and releasing it in free-fall before the science phase represents a single point of failure for the whole mission. This thesis describes the phenomena, operations, issues, tests, activities, and simulations linked to the release following a system engineering approach. Experimental studies have been carried out to investigate this phenomenon in conditions representative of the LISA-Pathfinder flight environment. The last part of the thesis is dedicated to the preliminary design of the housing of the TM in the frame of a low-cost mission conceived at Stanford (USA). The ambition of this work is increasing the maturity of the technology needed in drag-free projects and therefore provide a starting point for future fascinating and challenging missions of this kind.